1. Field of the Invention
The invention refers to a device for the metered administration and in particular the infusion of a fluid drug, comprising a container from which upon advancing a piston for administering said fluid drug the fluid drug is displaced in dosed manner through an outlet and a catheter connected to an outlet of said container, whose front end facing away from the outlet is connected to an injection needle, wherein a valve is positioned between the outlet and the injection needle in a flow cross section of the fluid drug and the valve, in order to prevent a self-discharge, only permits the flow to the front end of the catheter if the fluid pressure exerted in this direction exceeds a pressure on the valve caused by the dead weight of a fluid column in the device.
2. Description of the Related Art
In known infusion systems, the drug to be administered is stored in a container, normally an ampule, containing a carrier fluid in which the drug is dissolved—hereinafter referred to as fluid drug—between a movable piston and a container outlet. The rear end of a catheter is connected to the container outlet. The front catheter end contains an injection needle for administering the fluid drug into a human or animal body, which in most cases often remains there for the administration over several days. Where the fluid drug container is located at a greater height than the front end of the catheter or the needle, there is the danger that with sufficient height difference between the container and the front end of the catheter, the container could discharge itself as a result of the force of the fluid column.
In case of insulinisation, where portable infusion devices are used, i.e. pump devices, used catheters can exceed a length of 1 m. The longest catheter currently used with an infusion device has a length of some 1.1 m. Where the device with the container is vertically arranged above the user, i.e. during night time, this creates a hydrostatic base pressure of approx. 0.1 bar, if apart from the purely statistical pressure due to the dead weight of the fluid drug, no further effects such as frictional losses, discharge or capillary effects are considered and a density equal to that of water is assumed for the fluid drug.
In order to prevent the undesired discharge as a result of the fluid column pressure, the side friction between the piston displaceably arranged in the container and the container wall could be increased, which, however, would lead to other disadvantages. As a further solution the piston could be attached to the driven member, thus preventing a lowering of the fluid surface in the container and consequently a self-discharge. In known systems, the piston is screw-fitted to the driven member. This, however, adversely affects the cost of the device. This solution can also not be used for ready-to-use ampules as the piston is not prepared for a screw connection.